1. Field of the Invention
The present invention relates to an information processing apparatus in which a signal compression ratio is increased without deterioration in image quality by means of a selective thinning process in transmission of binary image signals obtained by scanning of an original document.
2. Description of the Prior Art
In a conventional facsimile apparatus as shown in FIG. 1, the black-and white information recorded on an original document, not shown, is converted, by scanning with a scanner A1, into time-serial binary image or picture signals consisting of a "0" signal representing a white or highlight dot and a "1" signal representing a black or shadow dot. A bandwidth compressor B1 compresses the binary image signals by alloting a code to each of the signals according to the run-length thereof. The thus coded signals are modulated by a modulator C1 into telephone line transmittable signals, i.e. AC signals within a determined frequency band width, and transmitted through a telephone line LT1.
In such facsimile apparatus it is not possible to expect a higher signal compression since the run-lengths of black or white picture elements are faithfully coded. There can be considered various processes, therefore, in order to improve signal compression ratio.
For example in the case of an existence of isolated spots, such as dusts or stains, on an original, the improvement in the compression ratio cannot be expected in the facsimile apparatus shown in FIG. 1 since such noise components are faithfully transmitted in such apparatus. For removing such noise components, therefore, there can be considered a process of eliminating such isolated spots.
Also in conversion of a boundary between black and white areas into binary image signals, there may often result so-called quantizing errors due to unstable identification of black or white levels. It is in fact not only meaningless but also detrimental to the improvement in the signal compression ratio to faithfully encode the binary image signals containing such quantizing errors.
In order to avoid such quantizing errors, there can be considered a smoothing process on such boundaries, which can be applied both in the principal or horizontal scanning direction (as represented by the arrow SC1 in FIG. 3A) and in the auxiliary or vertical scanning direction (as represented by the arrow SC2 in FIG. 3A).
Further, in image or picture information composed of letters, numerals, symbols etc. (hereinafter collectively called "characters"), it is difficult to improve the signal compression ratio is the line thickness is exactly coded despite of the fact that the line thickness of a character has no relation with the meaning thereof. However a socalled thinning process, which eliminates the information representing the line thickness and thus reduces the line thickness of black picture elements to a thickness of approximately one picture element, will inevitably lead to a deterioration in image quality. A more complicated structure of the apparatus though such a process will allow to improve the signal compression ratio. For example FIGS. 3A and 4A respectively show enlarged views of binary coded characters "mbre" and "fo". After the aforementioned elimination of isolated dots and smoothing followed by the aforementioned thinning process, the image quality will be significantly deteriorated as shown in FIGS. 3B and 4B. It will be understood that the character "r" in FIG. 3B lacks the portion P1, and the character "f" in FIG. 4B lacks the portion P2 or horizontal bar. Besides the thinned image as shown in FIG. 3B or FIG. 4B has to be thickened again in the facsimile receiver to obtain a restored image as shown in FIG. 3C or 4C, so that the apparatus inevitably bocomes complicated. For these reasons a signal processing without the drawbacks of the conventional thinning process has been longed for.